Electroslag ingot production

ABSTRACT

The electroslag process of ingot production in a mould is improved by providing bottom contact to the ingot via a stub or spigot provided at its bottom end.

United States Patent Inventor Peter Thomas Reginald Maskall Birmingham, England Appl. No. 701,653

Filed Jan. 30, 1968 Patented Sept. 28, 1971 Assignee Associated Electrical Industries Limited London, England Priority Feb. 7, 1967 Great Britain 5847-67 ELECTROSLAG INGOT PRODUCTION 8 Claims, 1 Drawing Fig.

US. Cl. 164/252, 13/ 1 6 int. Cl. 822d 27/02 Field of Search 164/52,

Primary Examiner-J.

Spencer Overholser Assistant Examiner-V. K. Rising Attorney-Bowyer & Witherspoon ABSTRACT: The electroslag process of ingot production in a mould is improved by providing bottom contact to the ingot via a stub or spigot provided at its bottom end.

ELECTROSLAG INGOT PRODUCTION Reference is made to prior patent to Maskall U.S. Pat. No. 3,448,790.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to the so-called electroslag process of producing ingots of metal, which word is used herein as conl noting not only elemental metals but also, in accordance with an important present day use of this process, metal alloys such for instance as various types of steel.

2. Description of Prior Art In such an electroslag process, an electrode of metal from which an ingot is to be produced, or possibly of unalloyed constituents of an alloy to be produced as an ingot, is supported with its lower end depending into an ingot mold and there immersed in a blanket of molten slag over a pool of molten metal. The lower end of the electrode is spaced from the surface of this molten pool and is progressively fused off to enter the pool by heat which is generated by the passage of electric current through the slag. The slag not only shields the metal pool from contaminating gases but can also be so chosen that it acts to segregate and absorb impurities from the molten metal in its passage through the slag from the electrode to the molten pool. The mold wall, and usually also the mold base, are continuously cooled, sothat, as the process proceeds, the molten metal solidifies progressively upwardly from the bottom and thereby fonns a progressively lengthening ingot which is separated from the mold at the end of the process.

In single-phase operation of the electroslag .process, (including the simultaneous formation of a number of ingots in individual molds with individual electrodes energized in parallel from a single-phase-line) and in multiphase, e.g., threephase, operation with individual molds (as distinct from multiphase modes of operation in which, with at least three electrodes in a single mold, the operation proceeds by virtue of electrode-ingot-electrode current flow without requiring electrical contact to the bottom of the ingot), the operation is dependent on continuity of current flow through the slag and the ingot metal between the electrode in the (or each) mold and a bottom contact to the ingot. Where, as is common, the mold base is used for providing the bottom contact to the ingot, trouble is sometimes experienced due to loss of electrical conduction between the bottom of the ingot and the mold base. Such loss of conduction is liable to occur if any sticking occurs between the ingot and the mold walls, because shrinkage of the cooling ingot between the mold base and the sticking location tends to cause the bottom of the ingot to lift off the base. As it is undesirable for electric current to flow in the mold walls, it is common practice to insulate the mold walls from the base in order to prevent such current flow. Therefore the shrinkage effect just described can result in the interruption of the process current and consequent stopping of the process. Moreover, immediately before such interruption of the current a hot spot or local arcing may develop at the last point of contact with the mold base and this may seriously damage the mold base.

Loss of conduction may also occur due to the formation, between the ingot bottom and the mold base, of a thin layer or skin of solidified slag the conductivity of which, over the whole or part of its area, has become so attenuated by cooling as to impair the operation of the process. Provided the slag which forms such a layer remains sufficiently hot, its conductivity is sufficiently high for the process to continue. However, as the ingot solidifies upwardly as the process progresses, there is a tendency for the slag layer to become cooler and to lose its high conductivity except where it is locally heated by current passing through a restricted region or region of its total area. Such region or regions may contract in size and/or reduce in number as the process continues, until either the current is interrupted or the localized heating produced by a high current flowing through a remaining region of relatively small area is sufficient to damage the mold base.

In the case of a multiphase operation in a single mold, the formation of the ingot can be concluded by a hot-topping procedure performed by withdrawing all but one of the electrodes and continuing the process in single-phase mode with the remaining electrode centralized in the mold, e.g., by appropriate sideways displacement of the latter on a wheeled support. In such a case, loss of bottom contact to the ingot during the multiphase operation could prevent the subsequent single-phase hot-topping step from proceeding. Moreover, loss of contact is more likely to occur with such multiphase operation than with single-phase operation, because in the latter the flow of current between the ingot bottom and mold base has some tendency to keep a thin slag film between the ingot and mold base in an electrically conductive state.

SUMMARY OF THE INVENTION According to the present invention maintenance of current connection to the bottom of the forming ingot is ensured by the provision at the bottom of the ingot of a stub or spigot which, being of material not incompatible with that of the ingot is received in a recess or opening for it in the mold base and has electrical connection made to it to provide bottom connection to the ingot, the cross section of the stub or spigot being smaller than the ingot cross section but being sufficiently great to carry the process current without fusing, taking into account any cooling effective on the stub or spigot.

Assuming the usual provision for making external electrical connection directly to the mold base, the stub or spigot can be arranged in heat and current transferring relationship with the mold base: the required bottom connection to the ingot is therefore ensured via the stub or spigot (cooled along with the mold base) even if the ingot bottom has lifted out of contact with the mold base or has become insulated from it by a slag skin.

By a material not incompatible with that of the ingot is mean one whose composition is the same as the ingot composition or at least is compatible with it.

BRIEF DESCRIPTION OF THE DRAWING The single FIGURE of the accompanying drawing is a somewhat schematic sectional elevation of an electroslag process mold showing the provision of an ingot bottom contact stub in accordance with the invention.

DESCRIPTION OF PREFERRED EMBODIMENT In the drawing, 1 represents the mold wall, (commonly but not necessarily cylindrical) insulated from the mold base 2 by insulating and sealing material 3. A water spray arrangement 4 round the top of the mold wall 1 produces a curtain 5 of cooling water which flows down the wall and is collected in a drainage trough 6 round the bottom of the wall. This trough 6 can with advantage be constructed as described in Maskall application, Ser. No. 629,746, now US. Pat. No. 3,448,790. The mold base 2 has a cooling jacket 7. For forming an ingot 8 by the electroslag process an electrode 9 (or a number of such electrodes) depends into the mold with the lower end dipping into a layer of molten slag 10. Electric current is passed through the slag and the forming ingot between the electrode 9 and a bottom connection to the ingot. (The manner in which this bottom connection is ensured in the illustrated arrangement will be described later.) The passage of the current through the slag 10 keeps it in its molten state and causes the electrode 9 to e progressively melted off at its lower end. The molten electrode material falls through the slag into a molten pool 11 at the top of the forming ingot. As the process proceeds the ingot progressively solidifies upwards from the bottom, due to the cooling of the mold. At the end of the process, the solidified ingot is separated from the mold.

In carrying out the invention there is the possibility of forming the mold base with a central recess having a depth significantly greater than the potential shrinkage of the ingot away from the mold base and of forming the stub or spigot in situ by allowing molten metal first to accumulate and solidify in this recess and thereby form the spigot or stub integrally with the subsequently solidifying main portion of the ingot.

The drawing, however, illustrates a preferred embodiment of the invention, for which a downwardly projecting boss 12 is formed on the underside of the mold base 2 in line with a central through-hole in it. This boss 12 terminates beneath the mold base in some suitable form of clamp 13 in which a preformed stub 14 of appropriate material, extending through the boss 12 into the bottom of the mold, can be mechanically gripped. The language into the bottom of the mold, as used in this specification mean that the stub terminates in the mold base or bottom member 2 but does not extend farther and into the mold cavity, this relationship being indicated in the drawing by the line 17. The clamp 13 also provides electrical connection between the stub 14 and the mold base 2 to which supply return conductors the are connected. (Supply connection, not shown, is also of course made to the electrode 9.)

The water-cooling jacket 7 for the mold base 2 has a large cen-' tral opening 16 through which the boss 12 passes with clearance. The boss is cooled by virtue of its integral attachment to the cooled mold base. Various other clamping and cooling arrangements can readily be envisaged and may be provided instead of that just described. For instance, the cooling jacket 7 may extend radially inwardly to the outer surface of the boss 12, which may then form the inner periphery of the cooling jacket so as to be directly cooled.

With the above arrangement the stub remains solid within the mold base and boss and becomes firmly welded to the ingot 8 (as indicated at 17) at the beginning of the formation of the latter. lf subsequently the ingot sticks in mold and the bottom of the ingot tends to lift by shrinkage, then either the stub 14 will be withdrawn slightly though the clamp 13 with the latter maintaining electrical connection, or the clamping When the ingot is ready for removal from the mold, the

clamp can be released and the stub can be withdrawn through the boss by (upward) withdrawal of the ingoLThe stub may then be cut off the bottom of the ingot and reused.

I claim:

1. An electroslag mold apparatus for melting an electrode within an electroslag mold, comprising, in combination:

a. a mold base having an upper wall, b. a mold wall upstanding from said mold base and forming a mold cavity c. an opening in said mold base, said opening having a cross section smaller than the internal cross section of said mold cavity, d. an electroconductive stub positioned within said opening and having an upper end, e. means for establishing electrical connection to said stub, f. said stub upper end being substantially flush with and substantially terminating at said upper wall, said apparatus being in claimed relationship prior to the start of the melting operation. 2. The apparatus of claim 1 and including a boss supported in depending fashion from said base, the said boss substantially surrounding said stub.

3. The apparatus of claim 2 and including a clamp supported on said boss, said clamp mechanically gripping said stub to provide electrical connection between said stub and said base. 7

4. The apparatus of claim 1 and including electrical conductive means mounted on said base and wherein said base is formed of electrically conductive material.

5. The apparatus of claim 2 and wherein the said boss is formed integrally with, and vertically extending downwardly from said base.

6. The apparatus of claim 1 and wherein said stub is a preformed element adapted for insertion in the said opening.

7. The apparatus of claim 1 and wherein said stub has both heat and current transferring relationship with said base.

8. The apparatus of claim 1 and wherein said stub is formed of a castable metal material. 

1. An electroslag mold apparatus for melting an electrode within an electroslag mold, comprising, in combination: a. a mold base having an upper wall, b. a mold wall upstanding from said mold base and forming a mold cavity, c. an opening in said mold base, said opening having a cross section smaller than the internal cross section of said mold cavity, d. an electroconduCtive stub positioned within said opening and having an upper end, e. means for establishing electrical connection to said stub, f. said stub upper end being substantially flush with and substantially terminating at said upper wall, said apparatus being in the claimed relationship prior to the start of the melting operation.
 2. The apparatus of claim 1 and including a boss supported in depending fashion from said base, the said boss substantially surrounding said stub.
 3. The apparatus of claim 2 and including a clamp supported on said boss, said clamp mechanically gripping said stub to provide electrical connection between said stub and said base.
 4. The apparatus of claim 1 and including electrical conductive means mounted on said base and wherein said base is formed of electrically conductive material.
 5. The apparatus of claim 2 and wherein the said boss is formed integrally with, and vertically extending downwardly from, said base.
 6. The apparatus of claim 1 and wherein said stub is a preformed element adapted for insertion in the said opening.
 7. The apparatus of claim 1 and wherein said stub has both heat and current transferring relationship with said base.
 8. The apparatus of claim 1 and wherein said stub is formed of a castable metal material. 